The　wastewater　treatment　process　(WWTP)　is　of　great　significance　to　environmental　protection.　To　improve　the　efficiency　of　the　WWTP,　it　is　crucial　to　ensure　that　the　dissolved　oxygen　(DO)　concentration　tracks　the　set　value　efficiently.　Due　to　the　nonlinear　and　time-varying　dynamics　of　the　WWTP,　traditional　control　methods　cannot　accurately　control　the　DO　concentration.　To　overcome　these　challenges,　this　paper　proposes　an　online　transferred　heuristic　dynamic　programming　(TrHDP)　control　design　by　combining　transfer　learning　with　adaptive　critic　design.　First,　we　use　the　historical　sample　data　to　construct　a　mathematical　model　of　the　WWTP　and　learn　the　prior　knowledge　from　the　model.　Then,　the　online　control　process　of　the　DO　concentration　is　guided　by　utilizing　the　prior　knowledge.　In　order　to　avoid　negative　transfer　and　save　computing　resources,　we　design　a　novel　decay　function　with　the　truncation　mechanism.　In　addition,　we　prove　the　stability　of　the　TrHDP　control　scheme　by　constructing　a　Lyapunov　function.　Finally,　the　performance　of　the　TrHDP　scheme　is　verified　by　the　Benchmark　Simulation　Model　No.　1.　Compared　with　other　methods,　the　TrHDP　method　possesses　higher　control　accuracy　for　the　DO　concentration　and　overcomes　the　disadvantage　of　low　learning　efficiency　of　general　online　methods.　IEEE